In this work, a closure experiment for tropospheric aerosol is presented. Aerosol size distributions and
single scattering albedo from remote sensing data are compared to those measured in-situ. An aerosol
pollution event on 4 April 2009 was observed by ground based and airborne lidar and photometer in
and around Ny-Ålesund, Spitsbergen, as well as by DMPS, nephelometer and particle soot absorption
photometer at the nearby Zeppelin Mountain Research Station.
The presented measurements were conducted in an area of 40 20 km around Ny-Ålesund as part of the
2009 Polar Airborne Measurements and Arctic Regional Climate Model Simulation Project (PAMARCMiP).
Aerosol mainly in the accumulation mode was found in the lower troposphere, however, enhanced
backscattering was observed up to the tropopause altitude. A comparison of meteorological data available
at different locations reveals a stable multi-layer-structure of the lower troposphere. It is followed by the
retrieval of optical and microphysical aerosol parameters. Extinction values have been derived using two
different methods, and it was found that extinction (especially in the UV) derived from Raman lidar data
significantly surpasses the extinction derived from photometer AOD profiles. Airborne lidar data shows
volume depolarization values to be less than 2.5% between 500 m and 2.5 km altitude, hence, particles in
this range can be assumed to be of spherical shape. In-situ particle number concentrations measured at
the Zeppelin Mountain Research Station at 474m altitude peak at about 0.18 mmdiameter, which was also
found for the microphysical inversion calculations performed at 850 m and 1500 m altitude. Number
concentrations depend on the assumed extinction values, and slightly decrease with altitude as well as the
effective particle diameter. A low imaginary part in the derived refractive index suggests weakly absorbing
aerosols, which is confirmed by low black carbon concentrations, measured at the Zeppelin Mountain as
well as on board the Polar 5 aircraft.